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Chip Amps Amplifiers based on integrated circuits

Power on/off 'Pop'
Power on/off 'Pop'
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Old 2nd July 2018, 10:10 PM   #1
Autotat is offline Autotat  United Kingdom
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Default Power on/off 'Pop'

Hello, I am hoping you fine folk might be able to help me with what I suspect may be a reasonably common problem.

I have a Cambridge Audio C500 pre-amp connected to a pair of Cambridge Audio P500 power amps that are Bi-amping a pair of floor standing speakers.

Whenever the pre-amp is switched on or off whilst the power amps are powered up there is a horrendous pop/thump through the speakers.

For a while the pre-amp was replaced with a Yamaha DSP E800 AV pre-amp with which it did not suffer this. Therefore I have naturually come to the conclusion that the Cambridge Audio pre-amp is the cause.

I am now looking to re-instigate the Cambridge Audio pre-amp as I no longer require surround sound and preferred the musical performance of the Cambridge unit.

Is there anything I can do to the pre-amp to fix this problem?

I am handy with a soldering iron but not too clued up on electronics. I have used the search function on this forum and found some threads but there appear to be a number of ways of tackling this and to be honest I got a bit lost.

Any help will be most greatfully recieved.

Thanks for reading.
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Old 2nd July 2018, 10:25 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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You need to trace back the pop signal and see where it starts.
It could be as simple as resistor from a capacitor ground to stop it putting out pops.
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Old 2nd July 2018, 10:32 PM   #3
Fenalaar is offline Fenalaar  Norway
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This pop is why you should always follow proper procedure when powering equipmen on or off. Power on should always start with the source and move towards the speaker. Power-off should start closest to the speaker and go towards the source.

Johan-Kr
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Old 2nd July 2018, 10:46 PM   #4
Autotat is offline Autotat  United Kingdom
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Thanks for the replies

Tracing the pop signal sounds fun, any pointers as to how to do this? SHould I be putting a multimeter across certain components and switching it on and off?
I believe I have a wiring diagram for the intergrated version of my amp combination somewhere, maybe that will give some clues.

Fenalaar - I ama aware of that, sadly the rest of the family (including one stropy teenage girl) doesn't treat it with the same respect.
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Old 2nd July 2018, 10:49 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Autotat View Post
Thanks for the replies

Tracing the pop signal sounds fun, any pointers as to how to do this? SHould I be putting a multimeter across certain components and switching it on and off?
I believe I have a wiring diagram for the intergrated version of my amp combination somewhere, maybe that will give some clues.

Fenalaar - I ama aware of that, sadly the rest of the family (including one stropy teenage girl) doesn't treat it with the same respect.
There could be two capacitors connected i.e. output of pre-amp and input of amp. You try a 4k7 to ground between them and see if that reduces pop.


Another source of pops is the mains switch. I had a disco turntable wit ha switch and every time it was turned on or off I got a huge pop through the speakers. I put 100nf 250VAC capacitor across the contacts and that reduced it massively.
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Old 2nd July 2018, 10:58 PM   #6
Autotat is offline Autotat  United Kingdom
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They both sound like much simpler fixes than the other posts I'd read, got to be worth trying first.

I have found the circuit diagrams for the intergrated version of the amps (A500) so will trawl thgough and identify the power supply diagram and try to decipher it.

Cheers.
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Old 5th July 2018, 11:32 AM   #7
Mooly is offline Mooly  United Kingdom
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Power on/off 'Pop'
Any competently designed stand alone preamp should have fool proof muting on the audio outputs to ensure 100% silent switch on and switch off.

You would have to study the Cambridge circuit to see whether any such facility exists (look for output relay/s or possibly transistors used for shunting the final audio output to ground).

It would also be worthwhile as a test to switch the preamp on/off via another method (wall outlet switch) to ensure that the noise isn't something being generated by the preamp mains switch itself.

Building a small muting circuit (relay and transistor to give a delay) is fairly easy but you would need to be able to adapt to suit.
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Old 5th July 2018, 04:29 PM   #8
Fast Eddie D is offline Fast Eddie D  United States
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Originally Posted by Mooly View Post
Any competently designed stand alone preamp should have fool proof muting on the audio outputs to ensure 100% silent switch on and switch off.
Agreed. And all you need is a shorting relay across the outputs that keeps the output shorted for about a second after turn on, and immediately shorts it on turn off. This can be accomplished with a simple 555 circuit.

Also capacitor across the on/off switch is required. I use a 47 nF/600 volt ceramic capacitor.

You can leave the power amp turned on and turn the preamp on and off and zero pops, clicks, or thumps.
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Old 5th July 2018, 06:09 PM   #9
tomchr is offline tomchr  Canada
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Even with a mute circuit in place, you can still have a small pop due to the charge injection of the switch or due to differences in DC offset between the source and the load. Those are obviously much, much lower than the typical rail-to-rail pops you get without the mute circuit, so the mute circuit does offer a significant improvement. I'm just saying that expecting power-up/down to be completely silent is a bit unrealistic.

Those interested in signal switching ought to read Doug Self's "Small Signal Audio Design". There's an entire chapter on signal switching and muting.

Tom
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Old 5th July 2018, 06:22 PM   #10
rayma is offline rayma  United States
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Originally Posted by Fast Eddie D View Post
Also capacitor across the on/off switch is required. I use a 47 nF/600 volt ceramic capacitor.
It's important to use an X capacitor which is rated for across the line.
http://www.kemet.com/Lists/Filestore...aRFIandSMD.pdf

Last edited by rayma; 5th July 2018 at 06:38 PM.
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